Surface mount electronic component

ABSTRACT

A surface mount electronic component includes an element including a dielectric layer that includes a first main surface and a second main surface, a first external electrode disposed on the first main surface, a second external electrode disposed on the second main surface, a first metal terminal connected to the first external electrode by solder, a second metal terminal connected to the second external electrode by the solder, and an exterior material covering at least a portion of the element, the first and second external electrodes, and the first and second metal terminals. The solder satisfies a relational expression: element diameter D (mm)×about 0.003 mm≤solder cross-sectional area S (mm2)≤element diameter D (mm)×about 0.02 mm.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to Japanese Patent Application No. 2017-035475 filed on Feb. 27, 2017. The entire contents of this application are hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a surface mount electronic component.

2. Description of the Related Art

For example, as an electronic component including an electronic component main body that is molded with a resin, the electronic components described in Japanese Patent Application Laid-Open Nos. S59-210632, 2011-9431, and 2007-81250 have been disclosed.

Japanese Patent Application Laid-Open No. S59-210632 discloses an electronic component which is connected to an electrode portion of a flat plate-shaped element having two electrode surfaces by soldering or the like and in which a protective coating material is coated thereon.

Further, Japanese Patent Application Laid-Open No. 2011-9431 discloses an electronic component in which lead-shaped metal terminals are connected to both sides of an electronic component element, a covering member that covers the electronic component element is provided, and the lowest point of a mounting portion of the metal terminal and the lowest point of the covering member are arranged substantially in the same plane.

Furthermore, Japanese Patent Application Laid-Open No. 2007-81250 discloses a radial lead type electronic component including an element portion coated with an insulating resin and two lead portions connected to the element portion and a surface mount electronic component including a case that internally accommodates the radial lead type electronic component.

However, in an electronic component as disclosed in Japanese Patent Application Laid-Open No. S59-210632, when electronic components are mounted, they are mounted by flow mounting or welding with lead wires inserted into a mounting board.

Accordingly, the electronic component cannot be mounted by reflow mounting in the first place.

Further, in an electronic component as disclosed in Japanese Patent Application Laid-Open No. 2011-9431, although surface mounting is possible, the flatness of a surface coated with a protective coating material is not sufficient. Thus, suction failure of a mounter of a mounting machine used to mount an electronic component on a mounting board occurs, the electronic component cannot be mounted on the mounting board, and mounting failure may occur.

Furthermore, although Japanese Patent Application Laid-Open No. 2007-81250 can solve the problem of Japanese Patent Application Laid-Open No. 2011-9431, the radial lead type electronic component is accommodated in the case, so that a problem occurs in which the height of a surface mount electronic component increases. Thus, in recent years, there are cases in which it is not possible to satisfy a requirement for miniaturization/height reduction of electronic components due to height reduction of electronic equipment. Further, since a process for accommodating electronic components in a case is required, the production cost increases.

Furthermore, similar to Japanese Patent Application Laid-Open Nos. S59-210632, 2011-9431, and 2007-81250, in a case in which an amount of solder is not suitable to bond an element and a metal terminal, when an electronic component is reflow-mounted, solder melts or expands to flow between a covering member (coating portion, coating material) and the element, and thus to connect between opposing external electrodes, wherein short-circuiting may occur in some cases.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide surface mount electronic components which enable reflow mounting to improve mountability and further reduce a height, and surface mount electronic components which significantly reduce or prevent short-circuiting.

A surface mount electronic component according to a preferred embodiment of the present invention includes an element including a dielectric layer that includes a first main surface and a second main surface, a first external electrode disposed on the first main surface, a second external electrode disposed on the second main surface, a first metal terminal connected to the first external electrode by solder, a second metal terminal connected to the second external electrode by the solder, and an exterior material covering at least a portion of the element, the first and second external electrodes, and the first and second metal terminals. In the surface mount electronic component, the first metal terminal includes a first bonding portion connected to the first external electrode, a first extending portion connected to the first bonding portion and extending in a direction parallel or substantially parallel to the first main surface with a space from the first main surface, a second extending portion connected to the first extending portion and extending toward the element, a third extending portion connected to the second extending portion and extending in the direction parallel or substantially parallel to the first main surface, a fourth extending portion connected to the third extending portion and extending in a mounting direction, and a first mounting portion connected to the fourth extending portion and mounted on a mounting board. The second metal terminal includes a second bonding portion connected to the second external electrode, a fifth extending portion connected to the second bonding portion and extending in a direction parallel or substantially parallel to the second main surface with a space from the second main surface, a sixth extending portion connected to the fifth extending portion and extending toward the element, a seventh extending portion connected to the sixth extending portion and extending in the direction parallel or substantially parallel to the second main surface, an eighth extending portion connected to the seventh extending portion and extending in the mounting direction, and a second mounting portion connected to the eighth extending portion and mounted on the mounting board. The solder satisfies a following relational expression: element diameter D (mm)×about 0.003 mm≤solder cross-sectional area S (mm²)≤element diameter D (mm)×about 0.02 mm.

In a surface mount electronic component according to a preferred embodiment of the present invention, the solder is preferably a lead-free solder having a high melting point.

In a surface mount electronic component according to a preferred embodiment of the present invention, preferably, upper and lower surfaces of the exterior material are flat or substantially flat. Further preferably, in the first bonding portion, a distal end of the first bonding portion is disposed in a direction away from the first main surface from an intermediate portion of the first bonding portion towards the distal end, and the first bonding portion is in surface contact with the first external electrode at the intermediate portion located on an opposite side of the distal end. Further preferably, a first cut-out portion is provided in a portion in which the second extending portion and the third extending portion of the first metal terminal intersect with each other. Further preferably, the second bonding portion includes a bifurcated distal end and is in surface contact with the second external electrode at the bifurcated portion. Further preferably, a second cut-out portion is provided in the fifth extending portion of the second metal terminal. Further preferably, a third cut-out portion is provided in a portion in which the sixth extending portion and the seventh extending portion of the second metal terminal intersect with each other. Furthermore preferably, the first to third cut-out portions are covered with the exterior material.

In a surface mount electronic component according to a preferred embodiment of the present invention, it is preferable that the first external electrode and the second external electrode include a first electrode layer made of a Ni—Ti alloy and a second electrode layer made of Cu.

In a surface mount electronic component according to a preferred embodiment of the present invention, the exterior material is preferably made of a thermosetting epoxy resin.

In a surface mount electronic component according to a preferred embodiment of the present invention, it is preferable that the element has a disk shape, a diameter of an outer shape of this element is not less than about 3.4 mm and not more than about 5.0 mm, and a thickness of this element is t=not less than about 0.90 mm and not more than about 0.95 mm.

With a surface mount electronic component according to a preferred embodiment of the present invention, the element on which the first external electrode and the second external electrode are arranged is supported not by a lead wire but by the first metal terminal and the second metal terminal and is able to be mounted on the mounting board by the first metal terminal and the second metal terminal, and therefore, mounting by reflow is made possible.

With a surface mount electronic component according to a preferred embodiment of the present invention, the first metal terminal includes the first bonding portion connected to the first external electrode, the first extending portion connected to the first bonding portion and extending in the direction parallel or substantially parallel to the first main surface with a space from the first main surface, the second extending portion connected to the first extending portion and extending toward the element, the third extending portion connected to the second extending portion and extending in the direction parallel or substantially parallel to the first main surface, the fourth extending portion connected to the third extending portion and extending in the mounting direction, and the first mounting portion connected to the fourth extending portion and mounted on the mounting board. In addition, the second metal terminal includes the second bonding portion connected to the second external electrode, the fifth extending portion connected to the second bonding portion and extending in the direction parallel or substantially parallel to the second main surface with a space from the second main surface, the sixth extending portion connected to the fifth extending portion and extending toward the element, the seventh extending portion connected to the sixth extending portion and extending in the direction parallel or substantially parallel to the second main surface, the eighth extending portion connected to the seventh extending portion and extending in the mounting direction, and the second mounting portion connected to the eighth extending portion and mounted on the mounting board.

With the above-described configuration, a case member as disclosed in Japanese Patent Application Laid-Open No. 2007-81250 is not required, and the shape of the metal terminal is optimized, so that an increase in the height dimension of the surface mount electronic component is prevented, and the height of the surface mount electronic component is able to be reduced.

With a surface mount electronic component according to a preferred embodiment of the present invention, the solder satisfies a following relational expression: element diameter D (mm)×about 0.003 mm≤solder cross-sectional area S (mm²)≤element diameter D (mm)×about 0.02 mm, and this relational expression is satisfied with respect to both of the solder bonding the first external electrode and the first metal terminal and the solder bonding the second external electrode and the second metal terminal. Accordingly, since a solder amount is set within an appropriate range, even if the solder melts or expands when the surface mount electronic component is reflow-mounted on the mounting board, flowing of the solder between the covering member (coating portion, coating material) and the element is reduced or prevented while bonding is secured, so that short-circuiting is prevented.

With a surface mount electronic component according to a preferred embodiment of the present invention, when the solder is a lead-free solder having a high melting point, while sufficient bonding strength between the element and the metal terminal is provided, heat resistance of the bonding portion to a flow or reflow temperature during mounting of the board is ensured.

With a surface mount electronic component according to a preferred embodiment of the present invention, if the upper and lower surfaces of the exterior material are flat or substantially flat, sufficient flatness is provided. Thus, it is possible to prevent suction failure of a mounter of a mounting machine used to mount the surface mount electronic component on the mounting board, and to reliably mount the surface mount electronic component on the mounting board. As a result, the occurrence of mounting failure is prevented.

With a surface mount electronic component according to a preferred embodiment of the present invention, in the first bonding portion, the distal end of the first bonding portion is disposed in the direction away from the first main surface from the intermediate portion of the first bonding portion toward the distal end, and when the first bonding portion is in surface contact with the first external electrode at the intermediate portion located on the opposite side of the distal end, an amount of the solder that intrudes between the first bonding portion and the first external electrode is increased. Therefore, the solder is able to be sufficiently caught between the upper surface of the first external electrode and the first bonding portion of the first metal terminal, and the bonding strength is increased.

In addition, the second bonding portion includes a bifurcated distal end, and when the second bonding portion is in surface contact with the second external electrode at the bifurcated portion, a contact area between the second metal terminal and the second external electrode is able to be increased, so that the element is stably supported with good posture by the second external electrode, and the bonding strength is increased.

With a surface mount electronic component according to a preferred embodiment of the present invention, when the first cut-out portion is provided in the portion in which the second extending portion and the third extending portion of the first metal terminal intersect with each other, the second cut-out portion is provided in the fifth extending portion of the second metal terminal, and the third cut-out portion is provided in the portion in which the sixth extending portion and the seventh extending portion of the second metal terminal intersect with each other, a flow path of the exterior material is secured when the exterior material is molded by injection molding, transfer molding, or the like, and the filling property of the exterior material is improved, so that an effect of improving withstand voltage performance, moisture resistance reliability, and other advantageous characteristics are achieved.

With a surface mount electronic component according to a preferred embodiment of the present invention, when the first external electrode and the second external electrode include the first electrode layer made of a Ni—Ti alloy and the second electrode layer made of Cu, it is possible to improve the bonding strength between the element and the second electrode layer by the first electrode layer in the first external electrode and the second external electrode, and to improve electroconductivity and ensure the bonding strength between the second electrode layer and the solder by the second electrode layer.

With a surface mount electronic component according to a preferred embodiment of the present invention, when the exterior material is a thermosetting epoxy resin, adhesion between the exterior material and the element or the metal terminal is ensured, and improved withstand voltage and moisture resistance performance are obtained.

With a surface mount electronic component according to a preferred embodiment of the present invention, the element has a disk shape, and when the diameter of the outer shape of the element is not less than about 3.4 mm and not more than about 5.0 mm, and the thickness of the element is t=not less than about 0.90 mm and not more than about 0.95 mm, since the shape of the element is optimized, the size and height of the surface mount electronic component is reduced.

Preferred embodiments of the present invention provide surface mount electronic components which allow reflow mounting to improve mountability and further reduce the height and surface mount electronic components which reduce or prevent short-circuiting.

The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an external perspective view showing an example of a surface mount electronic component according to a preferred embodiment of the present invention.

FIG. 2 is a top view of the surface mount electronic component shown in FIG. 1 showing a surface mount electronic component according to a preferred embodiment of the present invention.

FIG. 3 is a side view of the surface mount electronic component shown in FIG. 1 showing a surface mount electronic component according to a preferred embodiment of the present invention.

FIG. 4 is a perspective illustration view showing an internal structure of a surface mount electronic component according to a preferred embodiment of the present invention.

FIG. 5 is a cross-sectional view taken along line V-V in FIG. 4 showing a surface mount electronic component according to a preferred embodiment of the present invention.

FIG. 6 is a top view of FIG. 4 showing a surface mount electronic component according to a preferred embodiment of the present invention.

FIG. 7 is an external perspective view showing a state in which an exterior material is removed in a surface mount electronic component according to a preferred embodiment of the present invention.

FIG. 8A is a side view of FIG. 7 showing the state in which the exterior material is removed in a surface mount electronic component according to a preferred embodiment of the present invention, and FIG. 8B is an enlarged view of a bonding portion between a first bonding portion and a first external electrode.

FIG. 9 is a perspective illustration view showing a state in which an element is held by the first bonding portion of a first metal terminal and a second bonding portion of a second metal terminal in a surface mount electronic component according to a preferred embodiment of the present invention.

FIG. 10A shows a state in which an element is held by a conventional first metal terminal and a conventional second metal terminal, and FIG. 10B shows a state showing a result when the element is held by the conventional first metal terminal and the conventional second metal terminal.

FIG. 11 is an enlarged view showing a second mounting portion of a second metal terminal according to a preferred embodiment of the present invention.

FIG. 12 is a side view of a surface mount electronic component according to a preferred embodiment of the present invention and a view showing a mounting state of the first mounting portion of the first metal terminal and the second mounting portion of the second metal terminal.

FIG. 13 is a cross-sectional schematic view of a surface mount electronic component according to a preferred embodiment of the present invention and a view showing a relationship between a diameter D of an element and a cross-sectional area S of a solder.

FIG. 14 is an explanatory view for explaining a method of measuring the cross-sectional area S of the solder.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of surface mount electronic components according to the present invention will be described. FIG. 1 is an external perspective view showing an example of a surface mount electronic component according to a preferred embodiment of the present invention. FIG. 2 is a top view of the surface mount electronic component shown in FIG. 1 showing a surface mount electronic component according to a preferred embodiment of the present invention. FIG. 3 is a side view of the surface mount electronic component shown in FIG. 1 showing a surface mount electronic component according to a preferred embodiment of the present invention. FIG. 4 is a perspective illustration view showing an internal structure of a surface mount electronic component according to a preferred embodiment of the present invention. FIG. 5 is a cross-sectional view taken along line V-V in FIG. 4 showing a surface mount electronic component according to a preferred embodiment of the present invention. FIG. is a top view of FIG. 4 showing a surface mount electronic component according to a preferred embodiment of the present invention. FIG. 7 is an external perspective view showing a state in which an exterior material is removed in a surface mount electronic component according to a preferred embodiment of the present invention. FIG. 8A is a side view of FIG. 7 showing the state in which the exterior material is removed in a surface mount electronic component according to a preferred embodiment of the present invention, and FIG. 8B is an enlarged view of a bonding portion between a first bonding portion and a first external electrode.

A surface mount electronic component 10 according to a preferred embodiment of the present invention includes an element 12. The element 12 is preferably a single ceramic plate and has a disk shape, for example. The element 12 includes a first main surface 12 a and a second main surface 12 b facing each other and a side surface 12 c connecting the first main surface 12 a and the second main surface 12 b.

The surface mount electronic component 10 further includes an external electrode 14 disposed on the first main surface 12 a and the second main surface 12 b of the element 12, a metal terminal 16 connected to the external electrode 14 with a solder 40 interposed therebetween, the element 12, and an exterior material 18 covering at least a portion of the external electrode 14 and the metal terminal 16.

As a material of the ceramic plate, for example, a dielectric ceramic primarily including BaTiO₃, CaTiO₃, SrTiO₃, CaZrO₃, or other suitable dielectric ceramic may preferably be used. Further, it is also possible to use dielectric ceramics obtained by adding accessory components such as a Mn compound, a Mg compound, a Si compound, a Co compound, and a Ni compound to these main components. In addition, piezoelectric ceramics, such as PZT-based ceramics, semiconductor ceramics, such as spinel type ceramics, and other suitable ceramics may also be used.

Since the element 12 is preferably made of a dielectric ceramic, the element 12 functions as a capacitor. On the other hand, the element 12 functions as a piezoelectric component when a piezoelectric ceramic is used, and functions as a thermistor when a semiconductor ceramic is used.

Although the outer diameter dimension of the element 12 is not particularly limited, the diameter of the element 12 is preferably not less than about 3.0 mm and not more than about 6.0 mm, and more preferably not less than about 3.4 mm and not more than about 5.0 mm, for example.

Although the thickness of the element 12 is not particularly limited, it is preferably not less than about 0.8 mm and not more than about 1.2 mm, and more preferably not less than about 0.9 mm and not more than about 0.95 mm, for example.

The external electrode 14 is disposed on the first main surface 12 a and the second main surface 12 b of the element 12.

The external electrode 14 includes a first external electrode 14 a and a second external electrode 14 b.

The first external electrode 14 a is disposed on a surface of the first main surface 12 a of the element 12. The second external electrode 14 b is disposed on a surface of the second main surface 12 b of the element 12.

Although the size of the first external electrode 14 a is not particularly limited, it is preferable that the first external electrode 14 a is disposed on the entire or substantially the entire first main surface 12 a of the element 12. Similarly, although the size of the second external electrode 14 b is not particularly limited, it is preferable that the second external electrode 14 b is disposed on the entire or substantially the entire second main surface 12 b of the element 12. This makes it possible to alleviate electric field concentration as compared to a case in which a gap electrode is disposed, and an effect of improving withstand voltage performance is obtained.

As the material of the external electrode 14, for example, a metal such as Cu, Ni, Cr, Ag, Pd, Au, or Ti or an alloy containing at least one of these metals, such as Ag—Pd alloy, Cu—Ni alloy, Cu—Ti alloy, Ni—Cr alloy, or Ni—Ti alloy, may preferably be used. The external electrode 14 may be formed by laminating these metal materials.

In particular, the external electrode 14 preferably includes a first electrode layer (hereinafter referred to as Ni—Ti alloy layer) made of a Ni—Ti alloy and a second electrode layer (hereinafter referred to as Cu layer) disposed on a surface of the Ni—Ti alloy layer and made of Cu, for example.

In the external electrode 14, the Ni—Ti alloy layer and the Cu layer may alternately be provided in a plurality of layers.

For example, the external electrode 14 of the surface mount electronic component 10 may have a four-layer structure formed by alternately arranging the Ni—Ti alloy layers and the Cu layers. This makes it possible to obtain the effect of improving the bonding strength between the element 12 and the Cu layer as the second layer in the Ni—Ti alloy layer as the first layer. In the Cu layer as the second layer disposed on a surface of the Ni—Ti alloy layer as the first layer, electroconductivity is improved. In the Ni—Ti alloy layer as the third layer disposed on a surface of the Cu layer as the second layer, diffusion of the solder 40 and an oxide layer to an underlying electrode is reduced or prevented. In the Cu layer as the fourth layer disposed on a surface of the Ni—Ti alloy layer as the third layer, the bonding strength with the solder 40 is improved.

The external electrode 14 is preferably formed by electroless plating, vacuum film formation, sputtering or other suitable method, for example. Although the thickness of the external electrode 14 is not particularly limited, the thickness of the external electrode 14 is preferably not less than about 0.1 μm and not more than about 0.35 μm per layer, and the thickness of the entire external electrode 14 is preferably not less than about 0.7 μm and not more than about 1.2 μm, for example. Consequently, the thickness of the external electrode 14 is able to be reduced, and the height of the surface mount electronic component 10 is able to be reduced.

The metal terminal 16 is connected to the external electrode 14. The metal terminal 16 includes a first metal terminal 16 a and a second metal terminal 16 b.

The first metal terminal 16 a is connected to the first external electrode 14 a. The second metal terminal 16 b is connected to the second external electrode 14 b.

The metal terminal 16 is preferably a frame-shaped metal terminal, for example. Since the metal terminal 16 is a plate-shaped lead frame, the metal terminal 16 thus defined by a plate-shaped lead frame allows mounting on a mounting board, so that the surface mount electronic component 10 is able to be mounted by reflow.

The metal terminal 16 includes a terminal body and a plating film provided on a surface of the terminal body.

The terminal body is preferably made of Ni, Fe, Cu, Ag, Cr, or an alloy primarily including one or more of these metals, for example. Specifically, for example, the parent material of the terminal body may preferably be Fe-18 Cr alloy, Fe-42 Ni alloy, or Cu-8 Sn alloy (Here, numerals before the atomic elements mean the amount in weight percent (wt %), and applies hereafter). The thickness of the terminal body of the metal terminal 16 is preferably not less than about 0.05 mm and not more than about 0.5 mm, for example.

The plating film includes a lower layer plating film and an upper layer plating film. The lower layer plating film is provided on the surface of the terminal body, and the upper layer plating film is provided on a surface of the lower layer plating film. Each of the lower layer plating film and the upper layer plating film may include a plurality of plating films.

The lower layer plating film is made of Ni, Fe, Cu, Ag, Cr, or an alloy primarily including one or more of these metals, for example. The lower layer plating film is preferably made of Ni, Fe, Cr, or an alloy primarily including one or more of these metals, for example.

The upper layer plating film is made of Sn, Ag, Au, or an alloy primarily including one or more of these metals, for example. The upper layer plating film is preferably made of Sn or an alloy primarily including Sn, for example. When the upper layer plating film is made of Sn or an alloy primarily including Sn, solderability between the metal terminal 16 and the external electrode 14 is improved.

The thickness of the lower layer plating film is preferably not less than about 0.2 μm and not more than about 5.0 μm, for example. The thickness of the upper layer plating film is preferably not less than about 1.0 μm and not more than about 5.0 μm, for example.

When each of the terminal body and the lower layer plating film is made of Ni, Fe or Cr having a high melting point, or an alloy primarily including one or more of these metals, heat resistance of the external electrode 14 is improved.

The first metal terminal 16 a includes a first bonding portion 20 a connected to the first external electrode 14 a, a first extending portion 22 a connected to the first bonding portion 20 a and extending in a direction parallel or substantially parallel to the first main surface 12 a with a space t1 from the first main surface 12 a, a second extending portion 24 a connected to the first extending portion 22 a and extending toward the element 12, a third extending portion 26 a connected to the second extending portion 24 a and extending in the direction parallel or substantially parallel to the first main surface 12 a, a fourth extending portion 28 a connected to the third extending portion 26 a and extending in a mounting direction, and a first mounting portion 30 a connected to the fourth extending portion 28 a and mounted on the mounting board.

The second metal terminal 16 b includes a second bonding portion 20 b connected to the second external electrode 14 b, a fifth extending portion 22 b connected to the second bonding portion 20 b and extending in a direction parallel or substantially parallel to the second main surface 12 b with a space t2 from the second main surface 12 b, a sixth extending portion 24 b connected to the fifth extending portion 22 b and extending toward the element 12, a seventh extending portion 26 b connected to the sixth extending portion 24 b and extending in the direction parallel substantially parallel to the second main surface 12 b, an eighth extending portion 28 b connected to the seventh extending portion 26 b and extending in the mounting direction, and a second mounting portion 30 b connected to the eighth extending portion 28 b and mounted on the mounting board.

The first bonding portion 20 a of the first metal terminal 16 a is a portion connected to the first external electrode 14 a disposed on the surface of the first main surface 12 a of the element 12. In the first bonding portion 20 a of the first metal terminal 16 a, as shown in FIG. 8, it is preferable that a distal end 20 a 2 of the first bonding portion 20 a is disposed in a direction away from the first main surface 12 a from an intermediate portion 20 a 1 of the first bonding portion 20 a towards the distal end 20 a 2. It is preferable that the intermediate portion 20 a 1 (that is, a portion located on the opposite side of the distal end of the first bonding portion 20 a) of the first bonding portion 20 a is in surface contact with the first external electrode 14 a. Consequently, an amount of the solder 40 that intrudes between the first bonding portion 20 a and the first external electrode 14 a is increased. Therefore, the solder 40 is sufficiently disposed between the upper surface of the first external electrode 14 a and the first bonding portion 20 a of the first metal terminal 16 a, and the bonding strength is increased.

Although the distal end of the first bonding portion 20 a is disposed in a direction away from the first main surface 12 a from the intermediate portion of the first bonding portion 20 a toward the distal end, an angle α between a direction connecting the intermediate portion of the first bonding portion 20 a and the distal end and the upper surface of the first external electrode 14 a is preferably an angle of not less than about 1° and not more than about 5°, for example. Within this range, the bonding strength between the first external electrode 14 a and the first metal terminal 16 a is ensured.

The width of the first bonding portion 20 a of the first metal terminal 16 a is preferably not less than about 0.5 mm and not more than about 0.9 mm, for example.

The second bonding portion 20 b of the second metal terminal 16 b is a portion connected to the second external electrode 14 b disposed on the surface of the second main surface 12 b of the element 12. As shown in FIG. 9, the second bonding portion 20 b of the second metal terminal 16 b preferably includes a bifurcated (for example, wrench-shaped) distal end, and it is preferable that the second bonding portion 20 b is in surface contact with the second external electrode 14 b at the bifurcated portion. That is, preferably a space 20 b 1 is provided at a central portion of an end side opposite to a side connected to the fifth extending portion 22 b of the second metal terminal 16 b, provides a predetermined interval, and the second bonding portion 20 b is defined by one bonding piece 20 b 2 of the bifurcated shape and the other bonding piece 20 b 3. Consequently, a contact area between the second metal terminal 16 b and the second external electrode 14 b is increased. Thus, the element 12 is stably supported with good posture by the second external electrode 14 b, and the bonding strength is increased.

FIG. 10A shows a state in which an element is held by a conventional first metal terminal and a conventional second metal terminal, and FIG. 10B shows a result when the element is held by the conventional first metal terminal and the conventional second metal terminal. In a surface mount electronic component shown in FIGS. 10A and 10B, first and second external electrodes 2 a and 2 b are provided on both main surfaces of an element 1, a first external electrode 2 a and a first metal terminal 3 are connected to each other, and a second external electrode 2 b and a second metal terminal 4 are connected to each other.

If the shape of the second bonding portion 20 b is not the bifurcated shape (wrench shape) as in the present preferred embodiment but the conventional shape as shown in FIG. 10A, the center of gravity of the element 1 cannot be supported vertically, so that the element 1 may rotate. If the element 1 rotates, as shown in FIG. 10B, the element 1 is obliquely mounted with respect to a plane n parallel or substantially parallel to a mounting surface, so that there is a problem that a mounting height of the surface mount electronic component is increased.

The bifurcated shape of the distal end of the second bonding portion 20 b is not particularly limited to a wrench shape, and may be a U shape or a C shape, for example.

The entire width (width including both arms of the bifurcated shape) of the second bonding portion 20 b of the second metal terminal 16 b is preferably not less than about 2.3 mm and not more than about 2.7 mm, for example.

The first extending portion 22 a of the first metal terminal 16 a is connected to the first bonding portion 20 a and extends in the direction parallel or substantially parallel to the first main surface 12 a of the element 12 with the space t1 from the first main surface 12 a. In this manner, the first extending portion 22 a is disposed with the space t1 from the first main surface 12 a, wherein a flow path of the exterior material 18 is provided, and withstand voltage performance and moisture resistance performance are improved.

The width of the first extending portion 22 a of the first metal terminal 16 a is preferably not less than about 0.5 mm and not more than about 2.7 mm, for example. The length of the first extending portion 22 a is preferably not less than about 1.8 mm and not more than about 2.2 mm, for example.

In a portion of the first extending portion 22 a, a surface thereof is preferably structured into a concave shape, and the parent material of the first metal terminal 16 a may be exposed at the processed portion. Consequently, even if the solder 40 in the first bonding portion 20 a, for example, solder melts, since the wettability of the solder decreases due to exposure of the parent material of the first metal terminal 16 a at the concave-shaped processed portion, flowing out of the solder is blocked, so that flowing of the melting solder to the outside of the exterior material 18 is effectively reduced or prevented.

The fifth extending portion 22 b of the second metal terminal 16 b is connected to the second bonding portion 20 b and extends in the direction parallel or substantially parallel to the second main surface 12 b of the element 12 with the space t2 from the second main surface 12 b. In this manner, the fifth extending portion 22 b is disposed with the space t2 from the second main surface 12 b, wherein the flow path of the exterior material 18 is provided, and withstand voltage performance and moisture resistance performance are improved.

The width of the fifth extending portion 22 b of the second metal terminal 16 b is preferably not less than about 1.5 mm and not more than about 2.7 mm, for example. The length of the fifth extending portion 22 b is preferably not less than about 1.4 mm and not more than about 1.8 mm, for example.

In a portion of the fifth extending portion 22 b, its surface is preferably structured into a concave shape to provide a processed portion, and the parent material of the second metal terminal 16 b may be exposed at the processed portion. Consequently, even if the solder 40 in the second bonding portion 20 b melts, since the wettability of the solder decreases due to exposure of the parent material of the second metal terminal 16 b at the concave-shaped processed portion, flowing out of the solder is blocked, so that flowing of the melting solder to the outside of the exterior material 18 is reduced or prevented.

The second extending portion 24 a of the first metal terminal 16 a is connected to the first extending portion 22 a and extends toward the element 12. Specifically, the second extending portion 24 a is curved from a terminal end of the first extending portion 22 a and extends to a central portion of the element. For example, the curved portion may be gently curved, or may be curved such that the angle of the curved portion is substantially a right angle.

The width of the second extending portion 24 a of the first metal terminal 16 a is preferably not less than about 2.3 mm and not more than about 2.7 mm, for example. The length of the second extending portion 24 a is preferably not less than about 0.6 mm and not more than about 1.0 mm, for example.

The sixth extending portion 24 b of the second metal terminal 16 b is connected to the fifth extending portion 22 b and extends toward the element 12. Specifically, the sixth extending portion 24 b is curved from a terminal end of the fifth extending portion 22 b and extends to the central portion of the element. For example, the curved portion may be gently curved, or may be curved such that the angle of the curved portion is substantially a right angle.

The width of the sixth extending portion 24 b of the second metal terminal 16 b is preferably not less than about 2.3 mm and not more than about 2.7 mm, for example. The length of the sixth extending portion 24 b is preferably not less than about 0.6 mm and not more than about 1.0 mm, for example.

The third extending portion 26 a of the first metal terminal 16 a is connected to the second extending portion 24 a and extends in the direction parallel or substantially parallel to the first main surface 12 a of the element 12. Specifically, the third extending portion 26 a is curved from a terminal end of the second extending portion 24 a and extends in the direction parallel or substantially parallel to the first main surface 12 a. For example, the curved portion may be gently curved, or may be curved such that the angle of the curved portion is substantially a right angle.

The width of the third extending portion 26 a of the first metal terminal 16 a is preferably not less than about 2.3 mm and not more than about 2.7 mm, for example. The length of the third extending portion 26 a is preferably not less than about 1.0 mm and not more than about 1.4 mm, for example.

The seventh extending portion 26 b of the second metal terminal 16 b is connected to the sixth extending portion 24 b and extends in the direction parallel or substantially parallel to the second main surface 12 b of the element 12. Specifically, the seventh extending portion 26 b is curved from a terminal end of the sixth extending portion 24 b and extends in the direction parallel or substantially parallel to the second main surface 12 b. For example, the curved portion may be gently curved, or may be curved such that the angle of the curved portion is substantially a right angle.

The width of the seventh extending portion 26 b of the second metal terminal 16 b is preferably not less than about 2.3 mm and not more than about 2.7 mm, for example. The length of the seventh extending portion 26 b is preferably not less than about 1.0 mm and not more than about 1.4 mm, for example.

The fourth extending portion 28 a of the first metal terminal 16 a is connected to the third extending portion 26 a and extends in the mounting direction. Specifically, the fourth extending portion 28 a is curved from a terminal end of the third extending portion 26 a and extends in a direction of the mounting surface. For example, the curved portion may be gently curved, or may be curved such that the angle of the curved portion is substantially a right angle.

The width of the fourth extending portion 28 a of the first metal terminal 16 a is preferably not less than about 2.3 mm and not more than about 2.7 mm, for example. The length of the fourth extending portion 28 a is preferably not less than about 1.0 mm and not more than about 1.4 mm, for example.

The eighth extending portion 28 b of the second metal terminal 16 b is connected to the seventh extending portion 26 b and extends in the mounting direction. Specifically, the eighth extending portion 28 b is curved from a terminal end of the seventh extending portion 26 b and extends in the direction of the mounting surface. For example, the curved portion may be gently curved, or may be curved such that the angle of the curved portion is substantially a right angle.

The width of the eighth extending portion 28 b of the second metal terminal 16 b is preferably not less than about 2.3 mm and not more than about 2.7 mm, for example. The length of the eighth extending portion 28 b is preferably not less than about 1.0 mm and not more than about 1.4 mm, for example.

The first mounting portion 30 a of the first metal terminal 16 a is a portion connected to the fourth extending portion 28 a and mounted on the mounting board. Specifically, the first mounting portion 30 a is curved from a terminal end of the fourth extending portion 28 a and extends parallel or substantially parallel to the mounting surface. A gap portion 30 a 1 preferably having a rectangular or substantially rectangular shape is provided at a central portion of an end side opposite to a side connected to the fourth extending portion 28 a of the first mounting portion 30 a. Two mounting pieces 30 a 2 and 30 a 3 are arranged at the end side opposite to the side connected to the fourth extending portion 28 a of the first mounting portion 30 a with the gap portion 30 a 1 provided between the mounting pieces 30 a 2 and 30 a 3. In this manner, since the end side opposite to the side connected to the fourth extending portion 28 a of the first mounting portion 30 a is bifurcated into the mounting pieces 30 a 2 and 30 a 3 by the gap portion 30 a 1, even when the mounting piece 30 a 2 of the first mounting portion 30 a is deformed, the connection state is able to be maintained by the mounting piece 30 a 3. Similarly, even when the mounting piece 30 a 3 is deformed, the connection state is able to be maintained by the mounting piece 30 a 2, so that mounting reliability is maintained. Accordingly, if the first mounting portion 30 a is deformed in a state in which the gap portion 30 a 1 is not provided, there is a possibility that mounting reliability cannot be ensured, such as, not being able to be connected to the mounting board. In the first mounting portion 30 a, the gap portion 30 a 1 may not be provided.

As shown in FIG. 11, a plurality of small bending notches 30 a 4 and 30 a 5 are provided at portions of both ends in a connecting portion between the first mounting portion 30 a and the fourth extending portion 28.

This reduces physical resistance when the first mounting portion 30 a is bent, leading to a stable bending angle, and improved mounting reliability onto the mounting board is obtained.

In the first mounting portion 30 a, the bending notches 30 a 4 and 30 a 5 may not be provided.

As shown in FIG. 12, it is preferable that the first mounting portion 30 a is curved such that an extending angle β of the first mounting portion 30 a is not less than about 0° and not more than about 10°, for example, with respect to the mounting surface (horizontal surface). Consequently, it is possible to include an appropriate amount of solder fillet while ensuring installation reliability for mounting with a mounter, thus improving the mounting reliability.

The width of the first mounting portion 30 a of the first metal terminal 16 a is preferably not less than about 2.3 mm and not more than about 2.7 mm, for example. The length of the first mounting portion 30 a is preferably not less than about 0.3 mm and not more than about 0.7 mm, for example.

The second mounting portion 30 b of the second metal terminal 16 b is a portion connected to the eighth extending portion 28 b and mounted on the mounting board. Specifically, the second mounting portion 30 b is curved from a terminal end of the eighth extending portion 28 b and extends parallel or substantially parallel to the mounting surface. A gap portion 30 b 1 preferably having a rectangular or substantially rectangular shape, for example, is provided at a central portion of an end side opposite to a side connected to the eighth extending portion 28 b of the second mounting portion 30 b. Two mounting pieces 30 b 2 and 30 b 3 are arranged at the end side opposite to the side connected to the eighth extending portion 28 b of the second mounting portion 30 b with the gap portion 30 b 1 provided between the mounting pieces 30 b 2 and 30 b 3. Since the end side opposite to the side connected to the eighth extending portion 28 b of the second mounting portion 30 b is bifurcated into the mounting pieces 30 b 2 and 30 b 3 by the gap portion 30 b 1, even when the mounting piece 30 b 2 of the second mounting portion 30 b is deformed, the connection state is able to be maintained by the mounting piece 30 b 3. Similarly, even when the mounting piece 30 b 3 is deformed, the connection state is able to be maintained by the mounting piece 30 b 2, so that the mounting reliability is maintained. Accordingly, if the second mounting portion 30 b is deformed in a state in which the gap portion 30 b 1 is not provided, there is a possibility that the mounting reliability cannot be ensured, such as, not being able to be connected to the mounting board. In the second mounting portion 30 b, the gap portion 30 b 1 may not be provided.

A plurality of small bending notches 30 b 4 and 30 b 5 are provided at portions of both ends in a connecting portion between the second mounting portion 30 b and the eighth extending portion 28 b. This reduces physical resistance when the second mounting portion 30 b is bent, leading to a stable bending angle, and the improved mounting reliability onto the mounting board is obtained. In the second mounting portion 30 b, the bending notches 30 b 4 and 30 b 5 may not be provided.

As in the first mounting portion 30 a, it is preferable that the second mounting portion 30 b is curved such that the extending angle β of the second mounting portion 30 b is not less than about 0° and not more than about 10°, for example, with respect to the mounting surface (horizontal surface). Consequently, it is possible to include an appropriate amount of solder fillet while ensuring installation reliability for mounting with a mounter, thus improving the mounting reliability.

The width of the second mounting portion 30 b of the second metal terminal 16 b is preferably not less than about 2.3 mm and not more than about 2.7 mm, for example. The length of the second mounting portion 30 b is preferably not less than about 0.3 mm and not more than about 0.7 mm, for example.

It is preferable that the first metal terminal 16 a includes a first cut-out portion 32 a in a portion in which the second extending portion 24 a and the third extending portion 26 a of the first metal terminal 16 a intersect with each other. As shown in FIG. 6, the first cut-out portion 32 a is covered with the exterior material 18. Although the shape of the first cut-out portion 32 a is not particularly limited, it is preferable that the first cut-out portion 32 a has a rectangular or substantially rectangular shape, for example. The width of the first cut-out portion 32 a is preferably not less than about 0.4 mm and not more than about 0.8 mm, for example. The length of the first cut-out portion 32 a is preferably not less than about 1.0 mm and not more than about 1.4 mm, for example.

It is preferable that the second metal terminal 16 b includes a second cut-out portion 32 b in the fifth extending portion 22 b of the second metal terminal 16 b. As shown in FIG. 6, the second cut-out portion 32 b is covered with the exterior material 18. Although the shape of the second cut-out portion 32 b is not particularly limited, it is preferable that the second cut-out portion 32 b has a circular or substantially circular shape, for example. As the size of the second cut-out portion 32 b, the diameter is preferably not less than about 0.5 mm and not more than about 1.5 mm, for example.

It is preferable that the second metal terminal 16 b includes a third cut-out portion 32 c in a portion in which the sixth extending portion 24 b and the seventh extending portion 26 b of the second metal terminal 16 b intersect with each other. As shown in FIG. 6, the third cut-out portion 32 c is covered with the exterior material 18. Although the shape of the third cut-out portion 32 c is not particularly limited, it is preferable that the third cut-out portion 32 c has a rectangular or substantially rectangular shape. The width of the third cut-out portion 32 c is preferably not less than about 0.4 mm and not more than about 0.8 mm, for example. The length of the third cut-out portion 32 c is preferably not less than about 1.0 mm and not more than about 1.4 mm, for example.

The exterior material 18 is disposed to cover the element 12, the first external electrode 14 a, the second external electrode 14 b, a portion of the first metal terminal 16 a, a portion of the second metal terminal 16 b, a bonding portion between the first external electrode 14 a and the first metal terminal 16 a, and a bonding portion between the second external electrode 14 b and the second metal terminal 16 b.

The exterior material 18 preferably has a rectangular or substantially rectangular parallelepiped shape and includes a first main surface 18 a and a second main surface 18 b facing the first main surface 12 a and the second main surface 12 b of the element 12, a first side surface 18 c and a second side surface 18 d orthogonal to the first main surface 18 a and the second main surface 18 b and extending in a length direction (a direction in which the metal terminal 16 extends), and a first end surface 18 e and a second end surface 18 f orthogonal to the first main surface 18 a, the second main surface 18 b, the first side surface 18 c, and the second side surface 18 d. In the shape of the exterior material 18, a central portion of the thickness direction (directions of the first main surface 18 a and the second main surface 18 b) may be structured into a slightly convex shape along a circumferential direction. The shape of a corner portion of the exterior material is not particularly limited, and the corner portion may be rounded, for example. Specifically, it is preferable that the exterior material 18 is molded in a tablet shape having a diameter of not less than about 10 mm and not more than about 20 mm, for example.

The first main surface 18 a and the second main surface 18 b of the exterior material 18 are preferably flat or substantially flat.

Preferably, the material of the exterior material 18 is, for example, formed by coating a resin, such as a liquid or powder silicone or epoxy resin. As the material of the exterior material 18, an engineering plastic may be molded by an injection molding method, a transfer molding method, or other suitable method.

In particular, the material of the exterior material 18 is preferably made of a thermosetting epoxy resin, for example. Consequently, adhesion between the exterior material 18 and the element 12 or the metal terminal 16 is ensured, and improved withstand voltage and moisture resistance performance are obtained.

In the thickness of the exterior material 18, a thickness from a surface of the first external electrode 14 a of the element 12 to the first main surface 18 a of the exterior material 18 and a thickness from a surface of the second external electrode 14 b of the element 12 to the second main surface 18 b of the exterior material 18 are preferably not less than about 0.5 mm and not more than about 0.8 mm, for example. Further, a thickness from the side surface 12 c of the element 12 on the side closest to the first end surface 18 e of the exterior material 18 to the first end surface 18 e of the exterior material 18 and a thickness from the side surface 12 c of the element 12 on the side closest to the second end surface 18 f of the exterior material 18 to the second end surface 18 f of the exterior material 18 are preferably not less than about 1.3 mm and not more than about 2.5 mm, for example. Furthermore, a thickness from the side surface 12 c of the element 12 on the side closest to the first side surface 18 c of the exterior material 18 to the first side surface 18 c of the exterior material 18 and a thickness from the side surface 12 c of the element 12 on the side closest to the second side surface 18 d of the exterior material 18 to the second side surface 18 d of the exterior material 18 are preferably not less than about 0.2 mm and not more than about 1.4 mm, for example. Consequently, it is possible to secure required withstand voltage and reliability between the metal terminal 16 and the exterior material 18 while maintaining a small product size.

The first external electrode 14 a and the first metal terminal 16 a are connected by the solder 40, and the second external electrode 14 b and the second metal terminal 16 b are connected by the solder 40. The solder 40 is particularly preferably a lead-free solder having a high melting point, for example.

The lead-free solder having a high melting point is preferably a lead-free solder such as Sn—Sb based solder, Sn—Ag—Cu based solder, Sn—Cu based solder, or Sn—Bi based solder, and is more preferably a Sn-10Sb to Sn-15Sb alloy solder, for example. The lead-free solder having a high melting point is more preferably a Sn-13Sb alloy solder, for example. Consequently, heat resistance of a bonding portion during mounting is ensured.

As shown in FIG. 13, the solder 40 satisfies a relational expression “element diameter D (mm)×about 0.003 mm≤solder cross-sectional area S (mm²)≤element diameter D (mm)×about 0.02 mm”. This relational expression is required to be satisfied with respect to both of the solder 40 for bonding the first external electrode 14 a and the first metal terminal 16 a and the solder 40 to bond the second external electrode 14 b and the second metal terminal 16 b. According to the verification result, a minimum value of a thickness of a peeling portion was about 0.02 mm. In a case of “solder cross-sectional area S (mm²)>element diameter D (mm)×about 0.02 mm”, the solder volume exceeds the space size of the cross section, so that the solder reaches an electrode on the opposite side through an element side surface, thus leading to short-circuiting. On the other hand, in a case of “element diameter D (mm)×about 0.003 mm>solder cross-sectional area S (mm²)”, the thickness of the solder may be less than the unevenness of the element, and portions which do not come into close contact with each other are generated between the metal terminal 16 and the element 12, so that the bonding strength decreases.

From the viewpoint of bonding strength, it is preferable that the relational expression “solder cross-sectional area S (mm²)≤element diameter D (mm)×about 0.003 mm” is satisfied. Consequently, it is possible to ensure bonding between the external electrode 14 and the metal terminal 16.

In a method of measuring the cross-sectional area of the solder, the cross-section polishing is performed on the surface mount electronic component 10 including the metal terminals 16 to a position at which the width of the solder is largest, and the width and height of the solder are obtained from the cross section to calculate the cross-sectional area. For example, in a case of a shape of the second metal terminal 16 b, as shown in FIG. 14, the surface mount electronic component 10 is polished from the direction of the arrow A1, and the width and height of the solder at a position at which the area of the solder 40 is largest (a portion shown by a dashed line X1) are obtained to calculate the cross section. Alternatively, the surface mount electronic component 10 is polished from the direction of the arrow A2, and the width and height of the solder at a position at which the area of the solder 40 is largest (a portion shown by a dashed line X2) are obtained to calculate the cross section.

Further, regarding the method of measuring the cross-sectional area of the solder, a complicated shape of the distal end of the first bonding portion 20 a of the first metal terminal 16 a, more specifically, a portion at which the distal end 20 a 2 is disposed in the direction away from the first main surface 12 a as it approaches from the intermediate portion 20 a 1 of the first bonding portion 20 a towards the distal end 20 a 2 and the intermediate portion 20 a 1 (that is, a portion located on the opposite side of the distal end of the first bonding portion 20 a) of the first bonding portion 20 a is in surface contact with the first external electrode 14 a, is selected using a microscope, wherein the area is calculated from the number of pixels. On this occasion, the cross-section polishing is performed at a position at which the solder width is largest at each bonding portion.

The dimension in the length direction of the surface mount electronic component 10 (a direction in which the metal terminal extends) including the exterior material 18, the first metal terminal 16 a, and the second metal terminal 16 b is defined as the L dimension of the surface mount electronic component 10, the dimension in the thickness direction of the exterior material (a direction connecting the first main surface 18 a and the second main surface 18 b of the exterior material 18) is defined as the T dimension of the surface mount electronic component 10, and the dimension in the width direction of the exterior material 18 (a direction connecting the first side surface 18 c and the second side surface 18 d of the exterior material 18) is defined as the W dimension of the surface mount electronic component 10.

Although the dimensions of the surface mount electronic component 10 are not particularly limited, preferably, the L dimension in the length direction is not less than about 10.9 mm and not more than about 11.9 mm, the W dimension in the width direction is not less than about 5.5 mm and not more than about 6.5 mm, and the T dimension in the thickness direction is not less than about 2.3 mm and not more than about 2.5 mm, for example.

Next, a preferred embodiment of a method of manufacturing a surface mount electronic component having the above configuration will be described by taking the surface mount electronic component 10 as an example.

First, raw materials for manufacturing the element are provided and weighed.

Then, cobblestone is added to the raw material to be mixed and ground, and thus to be stirred, wherein the raw material is prepared.

Then, the prepared raw material is dried with a spray drier or other suitable drier.

Subsequently, an additive, a binder or other suitable material is added to the raw material to prepare a two-component raw material, and the two-component raw material is finely pulverized and then calcined.

Then, the calcined raw material is molded into a sheet shape by using an extruder or other suitable device.

Then, the sheet, which has been molded into a sheet shape, is punched into a disk tablet shape by using a press molding machine or other suitable machine. Then, the sheet punched into a disk shape is filled into a firing sagger, firing is performed, and the element 12 having a disk shape is manufactured. Although the firing temperature depends on a dielectric material, it is preferably not less than about 1100° C. and not more than about 1400° C., for example.

Then, the fired element 12 is set in a dry plating apparatus having a vacuum chamber, and the pressure is reduced.

Then, the element 12 in the reduced pressure atmosphere is preheated at a temperature of not less than about 50° C. and not more than about 150° C., for example. At this time, since the element 12 is preheated in a state of being set in a reduced pressure atmosphere having an atmospheric pressure of about 0.5 torr, even when the heating temperature is as low as not less than about 50° C. and not more than about 150° C., foreign matters such as moisture adhered to the element 12 are able to be removed efficiently.

Subsequently, when the preheating is completed, the interior of the vacuum chamber is evacuated again with a vacuum pump.

Then, the external electrodes 14 are formed on both main surfaces of the element 12 by a dry plating method, such as vacuum vapor deposition, sputtering, ion plating, or plasma spraying in a state in which the atmospheric pressure in the vacuum chamber is stabilized at not less than about 10⁻⁶ torr and not more than about 10⁻³ torr, for example.

The first metal terminal 16 a and the second metal terminal 16 b are prepared. The first metal terminal 16 a and the second metal terminal 16 b are molded by bending. The first cut-out portion 32 a formed in the first metal terminal 16 a and the second cut-out portion 32 b and the third cut-out portion 32 c formed in the second metal terminal 16 b are formed by punching.

First, the solder 40 is applied onto an upper surface of the second bonding portion 20 b of the second metal terminal 16 b (a surface facing the second main surface 12 b of the element 12).

Then, the element 12 on which the external electrode 14 is formed is inserted between the first metal terminal 16 a and the second metal terminal 16 b.

Subsequently, the solder 40 is applied onto a contact surface between the first metal terminal 16 a and the element 12.

Then, soldering is performed by reflow. As the soldering temperature, a heat of, for example, not less than about 270° C. and not more than about 300° C., for example, is preferably applied in reflow for not less than about 20 seconds.

Subsequently, in order to remove flux components included in the solder, ultrasonic cleaning using a solvent is performed. This is because if the flux remains attached, the adhesion between the exterior material 18 and the element 12 decreases, which causes a decrease in withstand voltage and moisture resistance performance.

Next, the exterior material 18 will be described. As the exterior material 18, an epoxy resin or other suitable material excellent in moisture resistance is used.

Then, the metal terminal 16 after flux cleaning treatment is fixed in a transfer mold die which has been preheated to a range of not less than about 170° C. and not more than about 190° C., for example.

Subsequently, a tablet-shaped epoxy resin is pressed into the die by a plunger at a pressure of not less than about 10 MPa and not more than about 20, for example, for about 60 seconds to form the exterior material 18 as shown in FIG. 1.

Then, after the exterior material 18 is formed, the metal terminal 16 protruding from the exterior material 18 is bent along the side surface and the bottom surface of the exterior material 18 to obtain the surface mount electronic component 10 shown in FIG. 1.

In the surface mount electronic component 10 shown in FIG. 1, the element 12 on which the external electrode 14 is disposed is supported not by a lead wire but by the metal terminal 16 and is able to be mounted on the mounting board by the metal terminal 16, and therefore, mounting by reflow is made possible.

Further, in the surface mount electronic component 10 shown in FIG. 1, the first metal terminal 16 a includes the first bonding portion 20 a connected to the first external electrode 14 a, the first extending portion 22 a connected to the first bonding portion 20 a and extending in the direction parallel substantially parallel to the first main surface 12 a with a space t1 from the first main surface 12 a, the second extending portion 24 a connected to the first extending portion 22 a and extending towards the element 12, the third extending portion 26 a connected to the second extending portion 24 a and extending in the direction parallel or substantially parallel to the first main surface 12 a, the fourth extending portion 28 a connected to the third extending portion 26 a and extending in the mounting direction, and the first mounting portion 30 a connected to the fourth extending portion 28 a and mounted on the mounting board. In addition, the second metal terminal 16 b includes the second bonding portion 20 b connected to the second external electrode 14 b, the fifth extending portion 22 b connected to the second bonding portion 20 b and extending in the direction parallel or substantially parallel to the second main surface 12 b with a space t2 from the second main surface 12 b, the sixth extending portion 24 b connected to the fifth extending portion 22 b and extending towards the element 12, the seventh extending portion 26 b connected to the sixth extending portion 24 b and extending again in the direction parallel or substantially parallel to the second main surface 12 b, the eighth extending portion 28 b connected to the seventh extending portion 26 b and extending in the mounting direction, and the second mounting portion 30 b connected to the eighth extending portion 28 b and mounted on the mounting board.

With the above-described configuration, the case member as disclosed in Japanese Patent Application Laid-Open No. 2007-81250 is not required, and the shape of the metal terminal 16 is optimized, so that an increase in the height dimension of the surface mount electronic component 10 is prevented, and the height of the surface mount electronic component 10 is reduced.

Further, in the surface mount electronic component 10 shown in FIG. 1, the solder 40 is satisfied by the relational expression “element diameter D (mm)×about 0.003 mm≤solder cross-sectional area S (mm²)≤element diameter D (mm)×about 0.02 mm”. This relational expression is satisfied with respect to both of the solder 40 for bonding the first external electrode 14 a and the first metal terminal 16 a and the solder 40 for bonding the second external electrode 14 b and the second metal terminal 16 b. Thus, since the solder amount is set within an appropriate range, even if the solder melts or expands when the surface mount electronic component 10 is reflow-mounted on the mounting board, flowing of the solder between the covering member (coating portion, coating material) and the element 12 is reduced or prevented while bonding is ensured, so that short-circuiting is prevented.

Further, with the surface mount electronic component 10 shown in FIG. 1, the first external electrode 14 a and the first metal terminal 16 a are connected by the solder 40, and the second external electrode 14 b and the second metal terminal 16 b are connected by the solder 40. When the solder 40 is a lead-free solder having a high melting point, while bonding strength between the element 12 and the metal terminal 16 is ensured, heat resistance of the bonding portion to a flow or reflow temperature during mounting of the board is ensured.

Further, in the surface mount electronic component 10 shown in FIG. 1, if the first main surface 18 a and the second main surface 18 b of the exterior material 18 are flat or substantially flat, sufficient flatness is ensured. Thus, it is possible to prevent suction failure of a mounter of a mounting machine used to mount the surface mount electronic component on the mounting board, and to reliably mount the surface mount electronic component on the mounting board. As a result, occurrences of mounting failure are effectively prevented.

Further, in the surface mount electronic component 10 shown in FIG. 1, the distal end 20 a 2 of the first bonding portion 20 a of the first metal terminal 16 a is disposed in the direction away from the first main surface 12 a from the intermediate portion 20 a 1 of the first bonding portion 20 a towards the distal end 20 a 2, and the intermediate portion 20 a 1 (that is, a portion located on the opposite side of the distal end of the first bonding portion 20 a) of the first bonding portion 20 a is in surface contact with the first external electrode 14 a. Therefore, the amount of solder 40 that intrudes between the first bonding portion 20 a and the first external electrode 14 a is increased. Therefore, the solder 40 can be sufficiently disposed between the upper surface of the first external electrode 14 a and the first bonding portion 20 a of the first metal terminal 16 a, and the bonding strength is increased.

In addition, the second bonding portion 20 b of the second metal terminal 16 b preferably includes a bifurcated (for example, wrench-shaped) distal end, and since the second bonding portion 20 b is in surface contact with the second external electrode 14 b at the bifurcated portion, the contact area between the second metal terminal 16 b and the second external electrode 14 b is increased, so that the element 12 is stably supported with good posture by the second external electrode 14 b, and the bonding strength is increased.

Further, in the surface mount electronic component 10 shown in FIG. 1, the first metal terminal 16 a includes the first cut-out portion 32 a in the portion in which the second extending portion 24 a and the third extending portion 26 a of the first metal terminal 16 a intersect with each other. Since the first cut-out portion 32 a is covered with the exterior material 18, the flow path of the exterior material 18 is provided when the exterior material 18 is molded by injection molding, transfer molding, or other suitable method, and the filling property of the exterior material 18 is improved, so that improved withstand voltage performance, moisture resistance reliability, and other characteristics are obtained.

In addition, the second metal terminal 16 b includes the second cut-out portion 32 b in the fifth extending portion 22 b of the second metal terminal 16 b, and the second cut-out portion 32 b is covered with the exterior material 18. The second metal terminal 16 b further includes the third cut-out portion 32 c in the portion in which the sixth extending portion 24 b and the seventh extending portion 26 b of the second metal terminal 16 b intersect with each other, and the third cut-out portion 32 c is covered with the exterior material 18. Therefore, a flow path of the exterior material 18 is provided when the exterior material 18 is molded by injection molding, transfer molding, or other suitable method, and the filling property of the exterior material 18 is improved, so that improved withstand voltage performance, moisture resistance reliability, and other characteristics are obtained.

With the surface mount electronic component 10 shown in FIG. 1, when the external electrode 14 includes the Ni—Ti alloy layer made of a Ni—Ti alloy and the Cu layer made of Cu and disposed on the surface of the Ni—Ti alloy layer, improved bonding strength between the element 12 and the Cu layer by the Ni—Ti alloy layer in the external electrode 14 is obtained, and improved electroconductivity and improved bonding strength between the Cu layer and the solder by the Cu layer are obtained.

With the surface mount electronic component 10 shown in FIG. 1, when the exterior material 18 is made of a thermosetting epoxy resin, the adhesion between the exterior material 18 and the element 12 or the metal terminal 16 is ensured, and improved withstand voltage and moisture resistance performance are obtained.

With the surface mount electronic component 10 shown in FIG. 1, the element 12 preferably has a disk shape, and when the diameter of the element 12 is not less than about 0.3 mm and not more than about 6.0 mm, and the thickness of the element 12 is not less than about 0.8 mm and not more than about 1.2 mm, since the shape of the element 12 is optimized, the size and height of the surface mount electronic component 10 are reduced.

Next, in accordance with the manufacturing method described above, a surface mount electronic component was manufactured, and experiments were conducted to confirm a short-circuit failure rate and a bonding strength failure rate. For the experiments, samples Nos. 1 to 6 in which the amounts of solder bonding the external electrode and the metal terminal were made different were provided. The number of samples for each sample number was set to 10 samples.

First, in order to produce the samples for each sample number, a surface mount electronic component having the following specifications was manufactured in accordance with the above-described method of manufacturing a surface mount electronic component.

Diameter of element: D value: about 3.4 mm

Thickness of element: about 0.95 mm

Material of element: BaTiO₃

Capacitance: about 330 μF

Rated voltage: about 300 V

Structure of external electrode: four-layer structure

-   -   Material of first electrode layer (first layer): Ni—Ti alloy     -   Material of second electrode layer (second layer): Cu     -   Material of first electrode layer (third layer): Ni—Ti alloy     -   Material of second electrode layer (fourth layer): Cu     -   Thickness of first electrode layer (first layer): about 0.2 μm     -   Thickness of second electrode layer (second layer): about 0.3 μm     -   Thickness of third electrode layer (third layer): about 0.2 μm     -   Thickness of fourth electrode layer (fourth layer): about 0.2 μm

Structure of metal terminal

-   -   Shape: as shown in FIGS. 5 and 6     -   Material of terminal body (parent material) of metal terminal:         SUS alloy     -   Plating film: Two-layer structure of Ni plating film (first         layer) and Sn plating film (second layer)

Exterior material

-   -   Material: Epoxy resin

Solder

-   -   Material: Sn-13 Sb alloy     -   For a solder area, see Table 1.

A method of measuring the solder area was as follows. The solder cross-sectional area S was measured by extracting the solder area with a microscope. At this time, cross-section polishing was performed to a position at which the solder width was largest in both the solder connecting the first external electrode and the first metal terminal and the solder connecting the second external electrode and the second metal terminal.

A method of confirming short-circuit failure was as follows. First, each sample was mounted on a glass epoxy substrate by using LF solder. Thereafter, a terminal of an IR meter (manufactured by HIOKI E.E. Corporation) was applied between the first electrode layer of the element and the second electrode layer of the element from the first metal terminal and the second metal terminal, and a sample of not more than about 1 GΩ was judged as a sample in which short-circuit failure occurred.

A method of confirming bonding strength failure was as follows. First, regarding the bonding strength, both side terminals were pulled in the vertical direction so as to move away from an element surface, and breaking strength at that time was measured. The pulling speed was about 10 mm/min. A breaking strength of not less than about 5N was judged as good, and a breaking strength of less than about 5N was judged as bad.

Table 1 shows experimental results of the confirmation of short-circuit failure and the confirmation of bonding strength failure.

TABLE 1 Solder cross- Solder cross- sectional Short- Bonding sectional area S/element circuit strength area S diameter D failure rate failure rate (mm²) (mm) (%) (%) Sample No. 1 0.0034 0.001 0 30 Sample No. 2 0.0102 0.003 0 0 Sample No. 3 0.034 0.01 0 0 Sample No. 4 0.068 0.02 0 0 Sample No. 5 0.102 0.03 10 0 Sample No. 6 0.17 0.05 20 0

In the samples Nos. 2 to 4, the solder amount is set to satisfy the relational expression: element diameter D (mm)×about 0.003 mm≤solder cross-sectional area S (mm²)≤element diameter D (mm)×about 0.02 mm. Accordingly, no short-circuit failure occurred, and no bonding strength failure occurred.

According to the above experimental results, the minimum value of the thickness of the peeling portion of the terminal and the element was about 0.02 mm. In the samples Nos. 5 and 6, there was a sample in which the short-circuit failure occurred. The reason for this is considered that in the samples Nos. 5 and 6, since the relational expression “solder cross-sectional area S (mm²)>element diameter D (mm)×about 0.02 mm” was satisfied, the solder volume exceeded the space size of the cross section, so that the solder reached an electrode on the opposite side through an element side surface, thus leading to short-circuiting.

On the other hand, in the sample No. 1, there was a sample having poor bonding strength. The reason for this is considered that in the sample No. 1, since the relational expression “element diameter D (mm)×about 0.003 mm>solder cross-sectional area S (mm²)” was satisfied, the thickness of the solder might be less than the unevenness of the element, and portions which did not come into close contact with each other were generated between the metal terminal and the element, so that the bonding strength decreased.

While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims. 

What is claimed is:
 1. A surface mount electronic component comprising: an element including a dielectric layer including a first main surface and a second main surface; a first external electrode disposed on the first main surface; a second external electrode disposed on the second main surface; a first metal terminal connected to the first external electrode by solder; a second metal terminal connected to the second external electrode by the solder; and an exterior material covering at least a portion of the element, the first and second external electrodes, and the first and second metal terminals; wherein the first metal terminal includes: a first bonding portion connected to the first external electrode; a first extending portion connected to the first bonding portion and extending in a direction parallel or substantially parallel to the first main surface with a space from the first main surface; a second extending portion connected to the first extending portion and extending towards the element; a third extending portion connected to the second extending portion and extending in the direction parallel or substantially parallel to the first main surface; a fourth extending portion connected to the third extending portion and extending in a mounting direction; and a first mounting portion connected to the fourth extending portion and mounted on a mounting board; the second metal terminal includes: a second bonding portion connected to the second external electrode; a fifth extending portion connected to the second bonding portion and extending in a direction parallel or substantially parallel to the second main surface with a space from the second main surface; a sixth extending portion connected to the fifth extending portion and extending towards the element; a seventh extending portion connected to the sixth extending portion and extending in the direction parallel or substantially parallel to the second main surface; an eighth extending portion connected to the seventh extending portion and extending in the mounting direction; and a second mounting portion connected to the eighth extending portion and mounted on the mounting board; and the solder satisfies a relational expression: element diameter D (mm)×about 0.003 mm≤solder cross-sectional area S (mm²)≤element diameter D (mm)×about 0.02 mm.
 2. The surface mount electronic component according to claim 1, wherein the solder is a lead-free solder having a high melting point.
 3. The surface mount electronic component according to claim 1, wherein upper and lower surfaces of the exterior material are flat or substantially flat; in the first bonding portion, a distal end of the first bonding portion is disposed in a direction away from the first main surface from an intermediate portion of the first bonding portion towards the distal end, the first bonding portion is in surface contact with the first external electrode at the intermediate portion located on an opposite side of the distal end; a first cut-out portion is provided in a portion in which the second extending portion of the first metal terminal and the third extending portion of the first metal terminal intersect with each other; the second bonding portion includes a bifurcated distal end and is in surface contact with the second external electrode at the bifurcated portion; a second cut-out portion is provided in the fifth extending portion of the second metal terminal; a third cut-out portion is provided in a portion in which the sixth extending portion of the second metal terminal and the seventh extending portion of the second metal terminal intersect with each other; and the first, second, and third cut-out portions are covered with the exterior material.
 4. The surface mount electronic component according to claim 1, wherein each of the first external electrode and the second external electrode includes a first electrode layer made of a Ni—Ti alloy and a second electrode layer made of Cu.
 5. The surface mount electronic component according to claim 1, wherein the exterior material is made of a thermosetting epoxy resin.
 6. The surface mount electronic component according to claim 1, wherein the element has a disk shape; a diameter of an outer shape of the element is not less than about 3.4 mm and not more than about 5.0 mm; and a thickness t of the element is not less than about 0.90 mm and not more than about 0.95 mm.
 7. The surface mount electronic component according to claim 1, wherein the element is a single ceramic plate.
 8. The surface mount electronic component according to claim 1, wherein the element is made of a dielectric ceramic primarily including at least one of BaTiO₃, CaTiO₃, SrTiO₃, and CaZrO₃.
 9. The surface mount electronic component according to claim 1, wherein the element is a capacitor.
 10. The surface mount electronic component according to claim 1, wherein the element has a disk shape; a diameter of an outer shape of the element is not less than about 3.0 mm and not more than about 6.0 mm; and a thickness t of the element is not less than about 0.80 mm and not more than about 1.2 mm.
 11. The surface mount electronic component according to claim 1, wherein each of the first and second external electrodes is made of at least one of Cu, Ni, Cr, Ag, Pd, Au, Ti, Ag—Pd alloy, Cu—Ni alloy, Cu—Ti alloy, Ni—Cr alloy, and Ni—Ti alloy.
 12. The surface mount electronic component according to claim 4, wherein each of the first external electrode and the second external electrode includes two of the first electrode layers and two of the second electrode layers that are alternately arranged.
 13. The surface mount electronic component according to claim 4, wherein a thickness of each of the first and second electrode layers is not less than about 0.1 μm and not more than about 0.35 μm.
 14. The surface mount electronic component according to claim 1, wherein a thickness of each of the first and second external electrodes is not less than about 0.7 μm and not more than about 1.2 μm.
 15. The surface mount electronic component according to claim 1, wherein each of the first and second metal terminals includes a terminal body and a plating film provided on a surface of the terminal body.
 16. The surface mount electronic component according to claim 15, wherein the terminal body is made of Ni, Fe, Cu, Ag, Cr, or an alloy primarily including one or more of Ni, Fe, Cu, Ag, and Cr.
 17. The surface mount electronic component according to claim 15, wherein a thickness of the terminal body is not less than about 0.05 mm and not more than about 0.5 mm.
 18. The surface mount electronic component according to claim 15, wherein the plating film includes a lower plating film provided on a surface of the terminal body and an upper plating film provided on a surface of the lower plating film.
 19. The surface mount electronic component according to claim 18, wherein the lower layer plating film is made of Ni, Fe, Cu, Ag, Cr, or an alloy primarily including one or more of Ni, Fe, Cu, Ag, and Cr.
 20. The surface mount electronic component according to claim 18, wherein the upper layer plating film is made of Sn, Ag, Au, or an alloy primarily including one or more of Sn, Ag, and Au. 